This invention constitutes a variation upon and refinement of applicant's earlier invention in the field of this invention, generally entitled "Air Ride Boad Hull". All of these inventions involve the introduction of pressurized gas in one or more recesses under a boat hull to augment hull lift and thereby improve hull load carrying capability, efficiency, ride quality and speed. The recess is bounded by one or more flexible seal members at its forward portion, downwardly extending members at its generally bow shaped aft portion and optionally therebetween, and by stabilizing, load carrying, catamaran-like side hulls that in the preferred embodiment may have diverging keels. The flexible seal at the front of the vessel in this invention absorbs much of the initial wave impact. The latter feature is intended to contribute substantially to the already exceptional ride qualities of vessels that incorporate Applicant's prior air ride inventions.
The combination of these elements is the aforementioned performance advantages over conventional hulls while offering operation, cost, and aesthetic advantages over other pressurized air hull craft. The invention taught herewith handles much like conventional hulls whether the pressurized gas supply is in use or not, costs only slightly more to manufacture and maintain than conventional hulls, and offers generally the same payload space, while maintaining most of the above water aesthetics of conventional hulls.
Even though the idea of introducing air or other gases at ambient or high pressures under boat hulls is not new in basic concept, only a few of the more sophisticated developments have met with any commercial success. However, due to their complex structural requirements and much larger flexible seals than that proposed in the present invention, these inventions generally remain too expensive or impractical for general marine application. The only example of the foregoing that is believed to have any applicability is the Surface Effect Ship (SES) as it is known in the United States. The SES is an outgrowth of the success of the Ground Effect Machine (GEM) as first made workable by Christopher Cockerell over two decades ago in England. The GEM is totally supported by an air cushion and has seals around its full periphery, and as such it is truly amphibious and has little relationship to this invention.
The SES is a marine vehicle with catamaran side hulls connected by a high, wide, cross structure at the top sides and by large flexible seals fore and aft. The SES offers superior ride qualities since the flexible seals yield resiliently to passing waves. However, because of the flexibility of the seals, and a generally flat undersurface, the hull cross structure is designed with a high wave clearing undercarriage. As a result, hull stresses can be very high and a highly stressed heavy hull cross structure is necessary. This is also aggravated by the fact that the SES must be much wider than the conventional hull or the air ride hull for stability purposes because of the SES's higher center of gravity (CG). As a result, even though the SES is very efficient, it compromises much of that advantage to expensive dead structure weight. A one hundred ten foot SES would have an undercarriage clearance of about eight feet and requires some forty feet beam for stability. A similar one hundred ten foot vessel made according to the present invention has a chamber depth of only about eighteen inches and a required beam of only some twenty-eight feet. The reason that the present invention requires so much less beam is because its deck load is only five to eight feet above the water compared to approximately twelve to fifteen feet for the SES because of the high wave clearing undercarriage made necessary by the form of the SES's structure.
However, due to its superior ride quality, very high speed capability, and high efficiency, the SES has received attention for naval and commercial application. This is reflected in extensive patent activity in this art. The most relevant examples include Ford, U.S. Pat. No. 3,146,752, using large flap-like seals fore and aft; Beardsley, U.S. Pat. No. 3,140,687; Mantle, et al., U.S. Pat. No. 3,476,069, which use more flexible fabric type seals fore and aft. The aforementioned inventions are substantially different from the present invention since they use flap-like or flexible seal members in the aft portion of the vessel, have a deep wave clearing undercarriage which utilizes much valuable hull space, have deep static draft requirements, require very wide beams for stability because of high CG characteristics, have inherently high stress hull structures that are heavy and expensive to manufacture, and cannot readily locate propellers under the aft flexible seal members due to vertical movement of the seals. Additionally, the flexible seals are heavy and expensive due to their large size and easy removal of the flexible seals for replacement or maintenance while the SES remains in the water is virtually impossible.
As noted above, the present invention is a derivation from Applicant's other inventive efforts with improved performance marine surface vessels that are in part supported by a pressurized gas layer structurally trapped and restrained beneath the hull. Prior patent filings of Applicant have centered upon vessels having a more or less conventionally shaped bow of hard structure. Actual test results utilizing a forty-two foot craft built in this manner show the viability of the forward bow member. The test vehicle, a forty-two by fifteen foot welded aluminum craft has achieved in actual practice substantial efficiency improvements as compared to conventional hull forms. Based on the test results, it can be said that, in moderate and heavy load carrying applications, conventional hulls will generally require from fifty to one hundred percent more power at planing speeds than a hull with concepts embodied in Applicant's prior inventions in this area. Additionally, the air ride invention normally realizes at least a thirty percent speed advantage. These performance advantages are similar to those experienced by the complex and vastly more expensive SES described above.
Since the bottom line on any commercial venture is cost, it should be considered that a one hundred ten foot off-shore oil industry crew and supply boat built to a conventional design would cost about 1.2 million dollars while a one hundred ten foot SES is in the four million dollar cost range. A one hundred ten foot air ride vessel built according to the present invention would cost thirty percent more than the conventional hull or about 1.6 million dollars. The air ride's higher speed and greater payload capability will pay back any of the cost difference between it and the conventional hull normally within the first year of operation. The difference between the 4 million dollar cost of a one hundred ten foot SES and the 1.6 million dollar for a one hundred ten foot vessel built according to the present invention is enough to cover fixed operating expenses less depreciation of the present invention for over fifteen years.